Mining and construction machines such as backhoe loaders and excavators employ various implements, such as buckets, rams, forks, grapples, thumbs, and the like, to perform different operations. For example, a machine may use a bucket and counteracting thumb to grasp, hold, and lift odd-shaped work material such as boulders, pipes, trees, structural components, and the like. These types of work material loads cause uneven weight distributions across the bucket and thumb and concentrated stresses on the components. A strong structure support that connects teeth of the thumb to the side plates and main body of the thumb may provide for more load transfer from one side of the thumb to the other. However, currently known structure supports for counteracting thumbs have structural and other limitations affecting their adaptation for various work environments in which the excavator machines may operate.
Some current thumb designs incorporate structure support that does not effectively transfer offset loads between the side plates of the thumb. For example, U.S. Pat. No. 5,813,822 to Pisco discloses a bucket and thumb combination for attachment to an excavator arm in which both the bucket and the thumb share a common axis of rotation relative to one another and relative to the excavator arm and are independently movable. The side plates and teeth of the thumb are connected by a structure support in the form of a flat plate. The flat plate is cheaper and easier to source worldwide than other types of structure supports such as circular and square tubes discussed below that can be dimensionally dependent on the region of sourcing. However, the flat connecting plate is not effective in transferring torque loads from the side plate with high concentration of loading to the side plate on the opposite side of the thumb. As a result, high stress concentrations occur on the loaded side of the thumb, thereby requiring thicker side plates on each side that add weight and cost to the thumb design.
Other thumb designs provide additional structure support but have other limitations that can compromise the design and integrity of the thumb. For example, U.S. Pat. No. 7,818,901 to Zeno et al. discloses a dipper stick, tool and thumb combination including a progressive linkage for connecting the thumb to a thumb actuator. The thumb disclosed in the Zeno et al. patent includes a circular tube as the structure support connecting the teeth of the thumb to the side plates. The tube may provide better load transfer between the side plates under offset load conditions than a flat plate, but the circular outer surface to which the side plates and the teeth are attached can present issues in supporting torsion loads that are created about the longitudinal axis of the circular tube. Torsion loads can occur when the bucket and thumb clamp down around work material with the teeth of the thumb engaging the work material. Due to the round surface of the tube, the amount of weld length between the circular tube and the side plates and teeth may not be sufficient given the space constraints of the design, and the torsion loads and resulting stresses may be concentrated at the welds connecting the teeth to the circular tube, and the circular tube to the side plates, making failures in the welds problematic.
Square tubes have been used in thumbs as an alternative to the circular tubes shown in the Zeno et al. patent. The square tubes may provide comparable load transfer between the side plates as the circular tubes, but create additional issues in designing and assembling the thumb. For example, in many implementations, the side plates and the teeth may mount on shared sides of the square tube causing an overlap in the structures. With the side plates infringing on the space for the teeth, interference with the side plates may inhibit the ability to place the teeth in the optimal locations along the tube. The square tube may also encroach the space within the thumb and interfere with the movement of the linkages that open and close the thumb.
For these reasons, a need exists for an improved structure support in a counteracting thumb of an excavation machine that assists in distributing unbalanced loads between the side plates of the thumb and bearing the loads and stresses on the teeth and side plates of the thumb without interfering with the free movement of the linkages controlling the location of the thumb.